The invention relates to the field of electronic reproduction technology for single color printing and is concerned with a method and an apparatus for the production of color separations for single color printing. What is meant by single color printing is, for example, textile, decorative, or packaging printing.
Whereas the inking of the print medium in polychromatic mixed or multicolor printing occurs by superimposed printing of different proportions of the inks "yellow", "magenta", "cyan", and "black", each color to be printed in single color printing is blended before the printing process and is then separately applied to the print medium, so that a corresponding color separation must be produced for every color of a color original.
Such a color original comprises, for example, hues having a progressive color distribution, i.e. having a different color saturation and/or luminance within the individual hues. In this case, the color separations must supply information regarding the topical distribution of the individual colors as well as information regarding the color progression, i.e. regarding the topically different intensity of the ink application.
An apparatus for the production of color separations for single color printing is already known from German Letters Pat. No. 26 28 053, corresponding to U.S. Letters Pat. No. 4,194,839, incorporated herein by reference. Three primary measured color value signals are acquired by means of opto-electronically scanning a color original point-by-point and line-by-line, said measured color value signals representing the color components, red, green, and blue of the scanned image points. A color recognition circuit receiving the measured color value signals, and in which a color recognition region for a color to be separated (separation color) in the color original is defined with a color space, selects the selected separation color from the other colors of the color originals during the scanning of the original and always generates a color recognition signal when the selected separation color is recognized in the color original. The color recognition signal is forwarded as a color separation signal to a recording element, for example a write lamp, whose brightness is modulated as a function of the color separation signal. The write lamp exposes a film as a recording medium point-by-point and line-by-line, said film representing the color separation for the selected separation color after it has been developed.
The known apparatus has the disadvantage that essentially only prismatic color recognition spaces can be defined or delineated. The color recognition spaces can therefore not be optimally matched in terms of size and shape to the color regions prescribed by the color progressions of the separation colors, the color separation signal thus not supplying an unequivocal statement regarding the color saturation and/or luminance of the separation colors.
Another apparatus for the production of color separations for single color printing is disclosed in German Letters Pat. No. 28 53 511, corresponding to U.S. Pat. No. 4,261,011, incorporated herein by reference. Given this apparatus, corrected color separation signals are derived from the measured color value signals and one of the corrected color separation signals is selected for recording a color separation for the single color printing. A color recognition signal which supplies a yes/no statement regarding the presence of the selected separation color in the color original is generated with the assistance of a color recognition circuit in which a color recognition space for the separation color is again defined. During recording of the color separation, the color recognition signal always connects through the selected, corrected color separation signal to the write lamp when the pre-set separation color is recognized in the color original. As a consequence of the switching, the color distributions in the color separations always appear sharply delineated, so that the individual separation colors are printed exactly side-by-side in the printing occurring later. This can occasionally lead to disturbing contours of color progressions in the print.
A modification of the above-described apparatus is known from European patent application No. 82112002.9, incorporated herein by reference, wherein the formation of such contours is in fact reduced, but a progressive color separation signal which exactly reproduces a color progression is nonetheless not generated therein.
All known apparatus also have the disadvantage that they are not specifically designed for the extraction of hues.